Which characteristic defines public goods?

Public goods are defined by two key characteristics: they are non-excludable and non-rivalrous. Non-excludable means that no one can be effectively excluded from using the good once it is provided, which typically leads to benefits for all members of society. Non-rivalrous indicates that one person's consumption of the good does not diminish the availability of that good for others. A classic example of a public good is national defense; once it is provided, everyone in the country benefits from it without preventing others from doing so.

The other characteristics listed do not accurately define public goods. While there may be market demand for public goods, that is not a defining feature of them. Likewise, limited availability or high production costs are not characteristics that distinguish public goods from private goods. Public goods can often be provided without limitation to their availability, challenging the notion of exclusivity and scarcity associated with private goods.